This invention relates to novel battery seals capable of prolonging shelf life of a battery by preventing moisture loss and oxygen ingress, while simultaneously providing a means for venting unusual amounts of gas build-up within the battery cell. The seal thus provides a safer, more effective means for containing a battery's necessary ingredients and/or preventing seepage of by-products of cell storage or discharge.
To provide a combination of functionality and safety, a battery seal should be capable of venting gases on rare occasions when, for reasons such as dead short, heavy load or unusual storage conditions, gas build-up becomes extraordinary. Under normal operating conditions, however, the seal should remain airtight.
It is known that the porous carbon rod of a typical zinc/carbon battery is capable of venting some excess gas. However, this may be quite insufficient when the battery is subjected to high heat or is otherwise used improperly. Porous seals, while able to handle the venting problem, would be undesirable for use as battery seals because they would not be expected to maintain sufficient airtightness under normal operating conditions. They would not, for instance, be expected to properly contain by-products of cell storage and discharge, nor to properly prevent moisture loss or oxygen ingress.
Plastic seals have been used on certain zinc/carbon dry cells, and asphalt has been used as a sealant between the plastic seal and the points within the battery where the seal makes contact. It is believed, for instance, that Matsushita manufactures zinc carbon dry cell batteries with an asphalt seal between the carbon pencil and a plastic seal washer, and that Matsushita has manufactured a product with asphalt at the interface between a seal washer and zinc can. Rayovac, and perhaps Matsushita, uses a solvent dissolved asphalt dispensed on the periphery of a shallow metal container to contact a closure cap and produce an airtight seal. Battery seals such as the Matsushita designs referenced above, however, would not be expected to provide a sufficient means for venting excess gases. A battery's inability to vent excess gas can cause rupture of the battery cell and can render the battery useless. Additionally, the build-up of pressure may, in some types of batteries, cause seepage of by-products and other materials which can be harmful to equipment into which the battery has been placed.
It is therefore an object of the present invention to provide an airtight battery seal which is capable of efficiently venting excess gases within a battery cell before the pressure of such gases reaches a level likely to cause rupture or seepage.
It is a further object of the invention to provide seals capable of venting gases in a non-destructive manner such that the battery remains functional after the venting.
It is a further object of the invention to provide a seal which prolongs battery shelf life by effectively preventing moisture loss from, or oxygen ingress into, the battery.
It is yet another object of the invention to provide a battery seal which is economical to manufacture and install, takes up less space than total asphalt overpour seals and is thoroughly reliable in use.